CS219022B1 - Process for producing a coagulating agent - Google Patents

Abstract

The purpose of the invention was to find a method for processing waste green slag heaps. This goal is achieved by preparing a solution with a maximum content of 10 g/l of free sulfuric acid from the heaped green slag and possibly also from acidic systems and supplementing it with fresh waste ferrous sulfate and a total iron content corresponding to at least 180 g Fe/l in the product. The solution prepared in this way is subjected to chlorination. The product is practically identical to ferric chlorosulfate and has the same area of application as ferric chloride.

Description

(54) Method for producing a coagulant

The purpose of the invention was to find a method for processing waste green slag heaps. This goal is achieved by preparing a solution with a maximum content of 10 g/l of free sulfuric acid from the heaped green slag and possibly also from acidic systems and supplementing it with fresh waste ferrous sulfate and a total iron content corresponding to at least 180 g Fe/l in the product. The solution prepared in this way is subjected to chlorination. The product is practically identical to ferric chlorosulfate and has the same area of application as ferric chloride.

The invention relates to a method for producing a coagulant based on trivalent iron.

Ferric chloride and ferric chlorosulfate are used as coagulants based on trivalent iron. Among these agents, ferrous sulfate can also be counted, in which trivalent iron as an active agent is formed only at the point of consumption by the simultaneous application of ferrous sulfate heptahydrate and chlorine. The most widely used of these agents is ferric chloride, in our country mainly in the form of solutions containing 180 to 200 g Fe/liter.

Ferric chloride is most often produced by reacting iron waste with a solution of ferric chloride. The resulting ferrous chloride is then re-oxidized with chlorine gas. The main part of the production costs is the cost of raw materials. The production is relatively simple, but inconvenient to handle.

The use of ferrous sulfate is complicated by the fact that its supply must be stored at the consumer's, which again results in unpleasant handling, because green slag quickly sinteres into hard blocks in piles. In addition, the user of green slag must have his own supply of chlorine, including an expensive gasification station with an operator, and also regulating the mutual ratio of chlorine and slag during dosing is not easy.

The production of ferric chlorosulfate solution starts from fresh ferrous sulfate, which is dissolved and oxidized with chlorine. Its use is similar to ferric chloride solution, so that the interchangeability of the two products does not cause any complications for the user. The production of chlorosulfate is a single-stage process — simpler than that of ferric chloride and is not accompanied by the formation of sludge.

The chlorine consumption per unit of ferric iron solution of the same concentration is only 1/3 of the amount necessary for the production of ferric chloride. Instead of expensive and scarce! iron scrap, green slag is processed, for which there is not enough use. All this makes this production very profitable.

At this point, it is also necessary to mention the problem of heaped green slag. Fresh waste green slag from the production of titanium white or from pickling steel with sulfuric acid is used for a number of purposes, including the above-mentioned use as a coagulant.

However, the long-term predominance of green slag production over its consumption has led to the necessity of storing this slag in large, expensive landfills, insulated against seepage into groundwater. Under the influence of atmospheric precipitation, part of the slag dissolves and the resulting solution must be pumped out. The pumped out solution is neutralized with milk of lime and pumped to a large sludge pond. The greater part of the piled slag has been lying in landfills for many years and is to a large extent oxidized and polluted with solid waste. No profitable use of this piled green slag has yet been found.

In titanium dioxide production plants, this problem is further compounded by the existence of so-called acid systems, which are iron(II) sulfates and other metals precipitated in the solid phase during the concentration of the cleavage acid from the titanium dioxide production by an immersion burner and separated on a rotary drum vacuum filter. These acid systems consist mainly of iron(II) sulfate monohydrate and contain up ^to 15% free sulfuric acid. The liquid phase contained in the acid systems is about 50% sulfuric acid. No profitable use has yet been found for these acid systems.

The above-mentioned disadvantages are not present in the method of processing acidic systems and waste heaped green slag into a coagulant based on trivalent iron according to the invention, which is characterized in that a solution containing a maximum of 10 g/liter of free acid is prepared from the heaped green slag containing at least 5% of total iron in trivalent form and optionally also from acidic systems, and after adding fresh waste ferrous sulfate to a total iron content corresponding to at least 180 g Fe/liter in the product, the solution or suspension is subjected to chlorination. The solution or suspension for chlorination can be prepared by adding fresh waste ferrous sulfate to the solution formed by dissolving the heaped green slag and optionally acidic systems by atmospheric precipitation or by spraying the heap with technological or suitable wastewater. Dissolving the piled waste green rock can also be done by repeatedly sprinkling the pile with a solution that has already seeped through the pile one or more times, or the dissolution of the piled waste green rock can be done with a solution or suspension of acidic systems.

The method according to the invention retains all the advantages of the production of ferric chloride sulfate, to which the following others are added: it is not necessary to use only fresh waste green slag for production, which may be in short supply in the future — the production of precipitated ferric pigments based on fresh waste green slag is being prepared. The oldest parts of the heaps can also be used for production, which will lead to their gradual liquidation, to prevent contamination of groundwater, to save costs for neutralizing solutions from the heap, to save costs for expanding heaps and sludge ponds, to prevent the occupation of new agricultural land. The existing heap can be used as part of the production equipment to carry out the method according to the invention. By using the solution formed on the heaps from atmospheric precipitation and its possible concentration by repeated seepage through the heap after spraying onto its surface, the necessary proportion of fresh waste rock for final saturation is reduced, and the consumption of chlorine is further reduced, because repeated seepage through the heap leads to enrichment with

β of the solution, especially on trivalent iron, so that the solution containing a significant proportion of iron in trivalent form, in contrast to the original technology, is used for chlorination.

Wastewater that can be used to dissolve waste heaped green slag can contain any amount of sulfuric acid and Fe ²⁺ and Fe ³⁺ ions. The relative content of dissolved impurities to total iron should not be greater than in acidic systems and the content of suspended solids should not be greater than 5 g/l.

The use of acidic systems brings further advantages. On the one hand, this simply valorizes the waste that these acidic systems create, for which there is no profitable use yet, and on the other hand, using acidic systems saves an even greater amount of chlorine than just using old heaps. After being flooded with water or a heap solution resulting from atmospheric precipitation, acidic systems react with old heap material in such a way that the reaction of free sulfuric acid in acidic systems with basic iron sulfates and/or with hydrated iron oxides or hydroxides returns these back to solution as Fe ³⁺ ions. This eliminates free sulfuric acid from acidic systems, which makes their other use difficult and complicates their disposal, and on the other hand, there is no need to perform repulping during their isolation to reuse sulfuric acid, which is difficult due to the poor filterability of acidic systems. However, this method mainly increases the concentration of iron in the chlorination solution, which leads to a further reduction in the necessary proportion of fresh waste green slag and, most importantly, the proportion of trivalent iron increases significantly, so that additional amounts of chlorine are saved and, finally, the degree of utilization of old heaps is increased, because not only water-soluble proportions but also trivalent iron in water-insoluble form is used.

When producing a solution of ferric chlorosulfate by the method known to date, 597 kg of FeSO ₄ .7H ₂ O, 327 kg of H ₂ O and 76 kilograms of Cl ₂ are required to produce a solution with a concentration of 180 g Fe/liter and a density of about 1.5 g/cm ³ (calculating for simplicity with pure substances per 1 ton of product).

If instead of water we use only the solution currently formed in heaps from atmospheric precipitation, 70 g/1 Fe ²⁺ , 15 g/1 Fe ^3h , h = 1.26 g/cm ³ , we need 428 kg FeSO ₄ .7 H ₂ O, 72 kg Cl ₂ and 500 kg of this solution for 1 t of product.

If we use a recycled solution, i.e. the above-mentioned solution, which we spray on the heaps or if we prepare the solution for chlorination by spraying water on the heaps in the dry season, so that we have a guarantee that all the water will seep through the heap (it will not rain into the liquid retention on the heap, nor onto free isolated areas), then we will obtain a solution for further work with a concentration of about 90 g/1 Fe ²⁺ and 46 g/1 Fe ³⁺ oh = 1.35 g/cm ³ . In this case, we need 325 kg FeSO ₄ .7 H ₂ O, 68 kilograms Cl ₂ and 607 kg of this solution for 1 t of the coagulant solution with 180 g/1 Fe.

If we use a solution that was created by the reaction of acidic systems, water and old parts of the heaps either directly on the heaps or by mixing in a tank and settling, we can expect the composition of the input solution to be approximately 70 g/l Fe ²⁺ and 75 g/l Fe ³⁺ at h = 1.4 g/cm ³ and the raw material consumption will be 221 kilograms of FeSO ₄ .7 H ₂ O + 51 kg Cl ₂ + 728 kilograms of this solution.

This means that when producing 40 kt/year of coagulant, the annual consumption would be:

FeSO ₄ .7 H ₂ O C1 ₂ solution a) 23,880 tons 3040 tons 13,080 tons b) 17,120 tons 2880 tons 20,000 tons c) 13,000 tons 2720 tons 24,280 tons d) 8,840 tons 2040 tons 29,120 tons Example 1 29.0 _{% Fe2} ( _SO4 ) ₃

690 kg of fresh evaporation green slag from titanium solutions with the following composition:

86.6

0.7

1.2

0.1

3.1%

% %

% %

8.3% _H2O

FeSO ₄ .7 H ₂ O

_Fe2 ( _SO4 ) ₃

TiOS0 ₄

MnSO ₄

MgSO ₄

11.6

0.1

2.1

0.8

0.1%

% %

% %

56.3%

FeCl ₃

_FeSO4

MgSO ₄

TiOSO ₄

MnSO ₄

_H2O

The coagulant solution prepared in this way contains 181.6 g Fe/L

Example 2 is mixed in a stirred tank with 270 kg H ₂ O and heated to 50 °C. The resulting suspension containing 13% solids is subjected to chlorination. During chlorination, 35 kg H ₂ O is evaporated.

A solution of the following composition is formed:

Rainfall falling on an isolated pool, on which individual heaps of green rock of various ages are placed, both flows down the bottom of the pool to the lowest places, and also seeps through the heaps of green rock to the bottom of the pool and flows down again. This creates a lagoon in a part of the pool containing a solution with the composition of, for example:

15.1 % _FeSO4 4.3 %: _Fe2 ( _SO4 ] ₃ 0.5 % TiOSO ₄ 1.5 o/o MgSO ₄ 0.1 O/o MnSO ₄ 78.5 O/o h ₂ o

465 kg of this solution is mixed in a stirred tank at 50 °C with 505 kg of the fresh waste green slag of the composition given in Example 1. The resulting suspension containing 6.7% solids is subjected to chlorination. During chlorination, 42 kg of H ₂ O is evaporated. A solution of the composition is formed:

29.4 o/o Fe ₂ (SO ₄ J ₃ 11.0% FeCl ₃

0.1 θ/ο FeSO ₄

2.3 o/o MgSO ₄ 0.8 θ/ο TiOSO ₄ 0.1% MnSO ₄

58.3% _H2O

The coagulant solution prepared in this way contains 180.45 g Fe/l.

Example 3

The process water is sprayed by a pump onto the surface of the older heaps so that it penetrates at least a 2- to 3-meter layer of green rock. It seeps through the heap and flows down the bottom of the pool to the lowest points, where it forms a lagoon from which the resulting solution can be pumped for further processing. This solution is not diluted with rainwater and has the following composition:

18.1% _FeSO4

10.6 θ/ο Fe ₂ (SO ₄ ) ₃ 0.8 θ/ο' TiOSO ₄ 2.1% MgSO ₄ 0.2% MnS0 ₄

68.2% _H3O

635 kg of this solution is mixed in a stirred tank at 50 °C with 340 kg of fresh waste green scale from titanium solutions mentioned in Example 1. The resulting solution is chlorinated. During chlorination, 39 kg of H ₂ O is evaporated. A solution with the following composition is formed:

31.0 o/o Fe ₃ (SOJ ₃ 9.8% FeCl ₃ 0.1% FeSO ₄

2.4 o/o MgSO ₄ 0.9 θ/ο TiOSO ₄ 0.2% MnSO ₄

55.6% _H2O

The coagulant solution prepared in this way contains 181.2 g Fe/l.

Example 4

The lagoon solution from Example 2 is pumped back onto the surface of the older greenstone heap and sprayed so that it permeates at least a 2- to 3-meter layer of greenstone. By re-permeating the heap, it is saturated to the concentration given in Example 3. Its further processing is the same as in Example 3.

Example 5

Acidic systems on composition

54.7% FeSO ₄ . H ₂ O 0.4% Fe ₃ (SO ₄ ) ₃

6.7% MgSO ₄ 4.0% TiOSO ₄ 0.1 θ/ο SiO ₂ 0.7 o/o MnSO ₄

15.5% _H2SO4 17.9% _{H2O is} immediately dissolved with water in a ratio of 1:1 after separation from the concentrated cleavage acid on a rotary vacuum filter, resulting in a suspension containing at 20°C 20% solid phase (mainly _FeSO4.7H2O , but also _insoluble impurities - _SiO2 and _TiO2 from partial hydrolysis of _TiOSO4 . This suspension is piped to the old heap and sprayed or poured onto its surface so that it seeps through at least a 2- to 3-meter layer of old heaped greenstone. By seeping through the heap, the solution is enriched with _Fe2 ( _SO4 ) ₃ contained in the heap, and by the action of _H2SO4 from acidic systems, a part of the basic iron( _III ) sulfates and/or iron(III) oxides or hydroxides contained in the heap is dissolved in insoluble form and a solution with the following composition is formed:

13.6% _FeSO4

19.7 «/o Fe ₂ (SO ₄ ) ₃ 0.7 «/o TiOSO ₄

1.6 v/v, MgSO ₄ 0.2 % MnS0 ₄

64.2 «/oh ₂ O

710 kg of this solution is mixed in a stirred tank at 50 °C with 260 kg of fresh waste green scale from titanium solutions mentioned in Example 1. The resulting solution is chlorinated. During chlorination, 21 kg of H ₂ O is evaporated. A solution with the following composition is formed:

33.3% _Fe2 ( _SO4 ) ₃

7.8% FeCl ₃ 0.1% FeSO ₄ 0.8% TiOSO ₄ 2.0% MgSO ₄ 0.2% MnS0 ₄

55.8 % H ₂ O

The coagulant solution prepared in this way contains 180.3 g Fe/l and a quantity of 1000 kilograms is shipped.

Example 6

740 l of _H2O are placed in a stirred rubber-lined container with a capacity of approximately 5 ^m3, 470 kg of acidic systems with the composition given in the previous example and 2470 kilograms of green slag from old oxidized parts of heaps with the composition:

35.6% _FeSO4

12.7% FeOHSO ₄ 1.0% TiOSO ₄ 0.2% MnSO ₄ 0.8% CaSO ₄ 0.1% SiO ₂

3.4% _MgSO4

46.2% _H2O

After thorough mixing, the monohydrate FeSO ₄ . H ₂ O from the acidic systems will be converted to the heptahydrate, and the free acid from the acidic systems will convert the basic iron sulfates into the solution. After 1 hour of mixing, the suspension is allowed to settle. A clear solution with the composition given in Example 5 in an amount of 710 kg is withdrawn, which is processed as given in this example. A solid phase containing excess FeSO ₄ .7 H ₂ O, insoluble components from the input raw materials, and partially hydrolyzed TiO ₂ will remain at the bottom of the vessel.

A certain proportion of MgSO ₄ is also drawn into the solid phase. The sediment at the bottom of the vessel contains 60% solid phase and 40% solution of the same composition as the solution withdrawn for further processing. The sediment is 2970 kg. The solid phase of the sediment has the composition:

87.7 % FeSO ₄ . 0.8 % _TiO2 4.8 % ^! MgSO ₄ 0.2 % MnSO ₄ 1.1 % _CaSO4 0.2 % SiO ₂ 5.3 % h ₂ 0

The sediment is removed from the vessel and placed on a heap, where it slowly undergoes oxidation and passes into solution by the action of atmospheric precipitation or artificial spraying and is treated similarly as indicated in the previous examples. The solution is chlorinated in the same way as in the previous example. The coagulant produced according to the invention is practically identical to ferric chlorosulfate and has the same field of application as ferric chloride or ferrous sulfate heptahydrate.

Claims (5)

SUBJECT 1. A process for the preparation of a trivalent iron coagulating agent, characterized in that a solution containing a maximum of 10 g / l of free acid is prepared from heaped waste green vitriol containing at least 5% of total iron in trivalent form and possibly from acidic systems and With a ferrous sulphate waste and a total iron content corresponding to at least 180 g of Fe / L in the product, the solution or suspension is led to chlorination. 2. A process according to claim 1, wherein the chlorination solution or suspension is prepared by adding fresh ferrous sulfate to the solution formed by dissolving the waste green vitriol and optionally acidic systems by atmospheric precipitation. 3. A process according to claim 1, wherein the chlorination solution or suspension is prepared by adding fresh ferrous sulphate waste to a solution formed by dissolving the heap green waste and possibly acidic systems by spraying the heap with process or waste water. 4. The method according to claim 1, 2 or 3, characterized in that the dissolution of the heap waste green vitriol is carried out by repeatedly sprinkling the heap with a solution which has leaked the heap one or more times. 5. A process according to claim 1 wherein the dissolution of the waste heaped green vitriol is carried out with a solution or suspension of acidic systems.